The use of towers for horizontal axis wind turbines is not recent, and its development has been boosted since the decade of 1980. For this type of wind turbine, the best use of the energy contained in the wind occurs with towers of greater height, since the wind is generally stronger and less turbulent under these conditions. The evolution of wind power generation technology has also brought greater dimensions to the components of known systems such as the rotor, tower and foundation. Towers that support wind turbines with a power of several megawatts currently have currently heights from 80 to 120 meters and above, and their structures are made of steel (tubular or trussed) or concrete (reinforced and/or prestressed). Also, exclusively tubular steel towers with heights exceeding 100 m and turbine outputs>2.0 MW are practically ruled out because of the transport width of the base segments (larger than 4.30 m in diameter). Therefore, for high towers (reaching 130 m hub height for a 5 MW wind turbine), the most economical solution presently is a hybrid tower design, consisting of a prestressed concrete tower (up to h=120 m) and a tubular steel top segment that supports the nacelle with the rotor.
Their bases are built with direct or indirect foundations made of concrete with large dimensions. Although the present concrete foundations meet the functions for which they are intended, with different types of format (square, polygonal, circular and annular), they account for big dimensions and a large volume of concrete and weight of reinforcement steel bars, due to the high moments transferred from the tower to the foundation base, at the around 280 cubic meters for towers of 80 meters height with turbines with a turbine having a nominal power of approximately 1.5 megawatts (passive reinforcement weighing about 17 tons), up to 1500 cubic meters for towers of 100 meters height with a turbine having a nominal power of around 5 megawatts (passive reinforcement weighing about 130 tons).
The large dimensions of wind farms and the large number of wind turbines, that have to be spaced apart by a minimum of the longitudinal extend of the tower and a distance three times the diameter of the rotor, are two of the most significant cost drivers during construction and operation of wind farms. Given these technical characteristics, bases for support existing wind turbine towers account for high costs of production, assembly, transportation and construction of wind turbine towers.
The foundation bases of the current wind turbine towers cause some inconveniences in the installation processes, such as:
large volume of excavation and backfilling due to the current dimensions of the foundation;
cost of reinforcement, material and labor;
longer production, transportation and execution time;
large volume of concrete required (may require refrigeration to combat thermal cracking);
large quantities of piles, when the geotechnical conditions of the site soil require deep foundations
All the above-mentioned items have significant impact in the wind park implementation costs (in the range of 20-30%), then many efforts and initiatives has been made by the wind park developers to minimize these costs. This is the main driver of the invention subjected to this process and described as follows.